Course threads on Hercus 260

I need to cut a decorative spiral with a 5mm pitch. My 260 will do a 5mm thread but I need to change some gears. For smaller threads you use the 18T gear. For larger threads you use the 45T gear. The gear that's not in use is used as a spacer on the bottom cluster. For the life of me I can't see how to swap the 18T and 45T gears. There doesn't seem to be room for the 45T gear as the setup stands. Can someone shed some light please?

Update:

I found the appropriate page in the Textbook Of Turning. Will work through that.

Did you get it Jack? You need to loosen the square head nut on the banjo and swing it down to gain the extra room. Sideways photo below.:doh:
Attachment 375287

Thanks Picko. Going to the shed now to have a crack at it.

All sorted. Easy when you know how!